First, I took note of the high general stress levels you guys have been under. So keep in mind that under those conditions we aren't always at our sharpest in thinking other things through. I suggest giving each other some slack in all this right now recognizing that you're both a little on edge to start with. If things get better (I hope) some of these conversations and issues will get easier to deal with. Don't try to take on too much change at once.

Also - looks like xmakina had several nice valid points there......
1> There's a LOT going on there
2> Getting in a 'good space' with you lover has to come first
3>Poly is really about strong, loving,honest relationships with multiple people But so is monogamy minus the extra people

But because everything is all confusing right now, let me see if we can just simplify it somewhat by breaking out the different elements to be thought about and addressed separately. If you can both get clear on things separately then you can see how they fit together after that.

Make sense ?

First - the sexual need mismatch. Or if you don't want to classify it 'sexual' the submissive desires. But I recommend you consider those desires sexual in nature. Maybe someone else will have a different take - we'll see. I just think it will help simplify the thought process if you do.
I can relate well to this because my mate has had somewhat similar needs in the past and it's not really my style either. A little play is fine & fun but I have my limits in taking on some dominant role over anyone - especially a woman. But I understand the desire fairly well and neither condone nor promote it. But in those games the critical thing is safety & trust. Because you love here YOU need to trust that's she's safe. SHE needs to trust whoever her partner is in that completely.
Now.......that deep a level of trust is definitely better - and much more easily built- from a truly loving perspective. Which will lead us to the next point.......

'Love' is a pretty slippery term and it has a lot of different meanings and ways of expression. You I think made some reference to 'romantic' love for example. So it might be good to note that if your mate required some form of 'love' to establish the necessary respect & trust to travel the BDSM path - that's not necessarily the same type of 'love' as the romantic love you have between you. But don't assume it couldn't take that turn either. But either way it's really not a threat. REALLY - it isn't.

Because..........
of the love you have for her and your desire for her happiness and fulfillment, by standing WITH her - partnering with her on finding happiness, you are EXPRESSING your true love for her ! It's more than words. It's actions.
These are the things that bind us Not words. Not concepts - or labels. Actions.
And what you build together out of love can never be threatened - except by yourselves.

So as you put it at the end - she wants a kink partner but in order for that to REALLY be benificial it needs to be based on trust and respect. Both important pieces of a loving relationship. And that's ok. It doesn't change what you have between you - UNLESS you do something to make it change. But supporting and helping can only make it change for the better - from my experience.